The present invention relates to soluble perhydrosiloxane copolymers of the formula [H.sub.2 SiO].sub.x [HSiO.sub.3/2 ].sub.y wherein the mole fractions x and y total 1. In addition the present invention relates to the use of these novel copolymers as coating materials especially for use on electronic devices.
Soluble hydridosiloxane polymers are known in the art. For instance, Collins et al. in U.S. Pat. No. 3,615,272 describe soluble hydrogen silsesquioxane resin of the formula [HSiO.sub.3/2 ].sub.n which is produced by the hydrolysis of a trichlorosilane, trimethoxysilane or triacetoxysilane in a hydrolysis medium formed by the reaction of concentrated sulfuric acid with an aromatic hydrocarbon.
Similarly, Japanese Kokai Patent 60[1985]-86017 describes a method of forming a soluble polydihydrogensil sesquioxane resin. This method comprises dissolving trichlorosilane in a previously water saturated solvent and then bubbling an inert gas accompanied by water vapor through the solution to hydrolyze and polycondense the silane. The resultant material was then silylated to form end-blockers.
Additionally, Wilcock et al. in U.S. Pat. No. 2,547,678 describe the production of linear, liquid dihydropolysiloxanes wherein substantially all of the valences o the silicon atoms between the terminal silicon atoms are satisfied by having two hydrogen atoms attached thereto. The method described therein comprises hydrolyzing halosilanes with an excess of water and recovering the polysiloxane.
Numerous hydridosiloxane copolymers are also known in the art. For instance, Johnson et al. in U.S. Pat. No. 3,992,426 describe a quadripolymer of the formula R.sub.3 SiO(R.sub.2 SiO).sub.a (RHSiO).sub.b (H.sub.2 SiO).sub.c SiR.sub.3. Additionally, Seyferth et al. in inorganic chemistry, Vol. 22 (1983), pages 2163-67 describe copolymers containing varying proportions of (H.sub.2 SiO), (CH.sub.3 SiHO) and [(CH.sub.3).sub.2 SiO].
The art also teaches that thin film ceramic coatings derived from hydrogen silsesquioxane resin can be applied on various substrates including electronic devices and circuits. For instance, Haluska et al. in U.S. Pat. No. 4,756,977 disclose silica coatings produced by applying a solution of hydrogen silsesquioxane to a substrate followed by conversion of the resin to silica by heating to temperatures of 200.degree.-1000.degree. C. The ceramic coatings produced by this method are taught to have many desirable characteristics such as microhardness, moisture resistance, ion barrier, adhesion, ductility, tensile strength, low electrical conductance and thermal expansion coefficient matching that make such coatings especially valuable.
The inventors herein have now discovered novel, soluble perhydrosiloxane copolymers described by the formula [H.sub.2 SiO].sub.x [HSiO.sub.3/2 ].sub.y which are useful for forming coatings on various substrates, especially electronic devices.